1. Field of Invention
This invention is related to toner for developing electrostatic images for use in electrophotography or electrostatic recording.
2. Description of Related Art
There are many known electrophotographic processes for recording an ink image on a recording medium. In these processes, an electrostatic latent image is formed on a photosensitive member by any suitable means. The electrostatic latent image is then developed with a toner. The resultant toner image is typically transferred to a recording medium, such as paper. The toner image is fixed on the recording medium by any suitable process, such as by heating, pressure application, treatment with a solvent vapor, or a combination thereof. The residual toner remaining on the photosensitive member is cleaned off the photosensitive member by any suitable means, such as by using a cleaning blade. The cleaning blade is typically comprised of a rubbery elastic material. The cleaning blade is pressed against the photosensitive member to clean the residual toner off the photosensitive member.
A small particle size toner is necessary to achieve high image quality. However, a small particle size toner is known to cause slippage, or passing-by, of the toner between the photosensitive member and the cleaning blade. Thus, the residual toner is not effectively cleaned off the photosensitive member by the cleaning blade.
Several techniques have been attempted to prevent slippage of the toner particles between the cleaning blade and the photosensitive member. These techniques include increasing the contact pressure between the photosensitive member and the cleaning blade, and increasing the coefficient of friction of the cleaning blade by changing the cleaning blade material. However, these techniques have failed for several reasons, such as breakage of the cleaning blade edge or filming of the photosensitive member.
A small particle size toner also tends to have a large triboelectric charge. The large triboelectric charge of small particle size toners inhibits transfer of the toner from the photosensitive member surface to an image recording medium, or from the photosensitive member surface to an intermediate transfer medium and from the intermediate transfer medium to the image recording medium. Accordingly, a toner should have a small particle size, as well as exhibit good cleanability and transferability. Various toner compositions are well known in the art, and have been produced having a wide range of additives and constituent materials. Generally, however, the toner particles include a binding material such as a resin, a colorant such as a dye and/or a pigment, and any of various additives to provide particular properties to the toner particles.
One type of additive that is commonly used in toner compositions is a surface additive. Toner surface additives are usually in the form of fine powders with primary particle sizes in the range of from about 5 to about 500 nanometers. The surface additive can be incorporated for any of various reasons, including for providing improved charging characteristics, improved flow properties, and the like.
For example, toner compositions with certain surface additives, including certain silicas, are known. Examples of these additives include colloidal silicas, such as AEROSILS like 972(trademark) available from Degussa, metal salts and metal salts of fatty acids inclusive of zinc stearate, aluminum oxides, cerium oxides, and mixtures thereof.
Sol-gel silicas have been discovered to impart additional advantages to xerographic developers that were not possible using conventional xe2x80x9cfumedxe2x80x9d metal oxides. Sol-gel silicas are silicas synthesized by the controlled hydrolysis and condensation of tetraethoxysilane. The sol-gel process is typically carried out in alcohol solvents with added homopolymer solutes to control the structure of the precipitated silicon dioxode product. Examples of alcohol solvents used in the sol-gel process include methanol, ethanol and butanol.
The transfer efficiency of toners treated with sol-gel silicas as external additives has been demonstrated to be superior to toners treated with xe2x80x9cfumedxe2x80x9d silica. The superiority of the sol-gel metal oxides is believed to be due to the spherical silica particles produced by the sol-gel process. One theory as to why this performance discrepancy exists is that inter-particle chain entanglements are evident for xe2x80x9cfumedxe2x80x9d silica particles, due to their branched structures. The spherical sol-gel silica particles, however, do not entangle.
While sol-gel silicas as toner surface additives have greatly improved transfer efficiency, particularly of small particles size toners, they have not been able to solve the filming and cleaning problems of small particle size toner. Sol-gel silicas, such as KE-P-10 and KE-P-30 silicas, available from Esprit Inc., as delivered, are not surface modified. The surfaces of sol-gel silicas typically contain a high amount of residual solvent, such as methanol and butanol, from the synthesis process. For example, the surface of the sol-gel silicas can contain upwards of 10 wt % of methanol and butanol. Removal of the residue on sol-gel silicas is necessary for effective surface treatment and, thereafter, for the proper cleaning and filming performance of the prepared toner.
The present invention addresses these problems by using, as a toner particle surface additive, a treated sol-gel silica or other sol-gel metal oxide. Use of the treated sol-gel metal oxide provides significant benefits to the toner compositions. The treated sol-gel metal oxide allows for improved cleaning of residual toner from the photosensitive member. The treated sol-gel metal oxide also prevents filming of the photosensitive member.
In particular, the present invention provides a toner composition including a binder, a colorant, and sol-gel metal oxide particles surface-treated with a treatment agent.